Kinetics and mechanism of the reaction of iron with sulfur vapor in the temperature range of 250 to 500°C

The kinetics and mechanism of the reaction between iron and sulfur vapor were investigated in the temperature range of 250 to 500°C and sulfur vapor pressures of 10 to 300 mm Hg. The sulfurization of iron has been found to follow a parabolic law. In the temperature range 250 to 370°C the reaction product consisted of an inner FeS scale, and an outer thin FeS 2 layer. The activation energy of this process amounts to 27 kcal/mole, and the parabolic reaction rate constant varies according to approximately the 1/2 power of the sulfur pressure. In the temperature range 370 to 500°C the reaction product consists entirely of an FeS scale. The activation energy of the limiting process in this temperature range is about 14 kcal/mole. The parabolic reaction rate constant at 500°C shows a sulfur pressure dependence according to approximately the 1/7 power of the sulfur vapor pressure. The mechanistic significance of the experimental results is considered in some detail.